A few months later, I’d heard he’d moved to the Midwest. I got a more comprehensive report from mutual friends who’d gone out there: He had a job at a local paper, had a new band and was doing “really well.” And lived in “an awesome house.” With “really cool roommates.” He “knew everyone in town.” (Already?!)

I was happy for him, but there was also a little teensy part of me that felt whatever the opposite of schadenfreude is—instead of feeling happy at someone’s misfortune, I felt resentful at someone’s good fortune. Why couldn’t he have gotten his proverbial shit together while we were dating? And, a more uncomfortable thought: Was it somehow my fault? Maybe, I realized, I had seen him as someone who had potential but just needed a little tweaking. But it was sort of annoying that he managed to do all the tweaking after we’d broken up.

It’s the Butterfly Effect: one day he’s a pot-addled caterpillar barely hanging on to his barista job, begging off brunch because he’s only got $37 in his checking account, spending his nights “playing music” (his band is going to start playing shows again really soon) and eating cheese fries, and then, six months after the breakup, he’s turned into a Monarch: lost 20 pounds, has a job as a graphic designer, his band is playing the Bowery Ballroom and he has a new girlfriend (tall, blond, wearing what appears to be the $282 Vanessa Bruno sweater you eyed longingly at Stuart & Wright) who, he casually mentions when you run into him at brunch, is the heiress to a paper clip fortune.

So in the spirit of Valentine’s Day, I asked some female acquaintances whether they’d ever experienced the Butterfly Effect. A few claimed the reverse: “No, my loser boyfriends have all stayed losers after we broke up,” said one. Another told me: “I make ’em good, then they go downhill after we break up,” pointing to an ex who works in human resources in a dingy town in upstate New York. And a third: “I do have the phenomenon of men hitting bottom after they date me, which is delicious/sad/rewarding. … It’s somewhat comforting to know that they ‘peaked’ with me.”

Other ladies, however, were all too familiar with the phenomenon. Michelle, a 26-year-old law student, told me about a guy she dated in college named Steve who was “hot as hell,” but “wasn’t particularly brilliant.” He was on the wrestling team on scholarship, but quit soon after they’d started dating. “He was a pre-med major but got mostly C’s, so he definitely wasn’t going to become a doctor. I convinced him to switch to history/pre-law. I remember editing one of his 20-page papers—it took me 11 hours. It was awful.”

Thanks to Michelle’s help, Steve’s grades improved. He took the LSATs “a few times to get a good enough score to get into a decent law school,” and, said Michelle, “I didn’t think anything of it”—until a couple years later, when she found out he’d graduated at the top of his class, was editor of the law review and got a job at “an incredible international law firm. He was completely floundering when we were dating, and now all he does is work and succeed. No idea how that happened!”

Michelle’s relationship hews to a common pattern, in which the woman, seeing the man as a project, tries to “improve” him, thereby leading to resentment in the relationship when the woman feels that the man is not improving enough, and the man feels emasculated and condescended to.

(Not that I’m speaking from experience or anything.)

Liz (not her real name), a 31-year-old writer who lives in Brooklyn, had a similar relationship with Josh. “I was always actively trying to improve him,” said Liz. “He had been really depressed and wasn’t going to therapy. And I was finally like, you really have to go back. And he was like, I know, but I’m never going to make the appointment. So I found a therapist and made an appointment. So I felt this sense of self-worth—I’m the girl that’s making this guy happier.”

Liz also took on Josh’s employment prospects. “He was always asking me to do a résumé and cover letter, but that’s, like, the least sexy thing I can imagine. I don’t even want to do that if someone pays me a lot of money! But I finally did. Then that night, we went to dinner, and he was like, ‘I’m seeing other people.’ I don’t know if he specifically waited to tell me that after I had helped him make a résumé and cover letter, but it kind of felt like that. And even though it was in the middle of a recession, he quit his job without having a new job and used my brilliant cover-letter and résumé-writing skills to get a new job—within two weeks!”

Another version of the Butterfly Effect is the woman who shows a guy the ropes, and is shocked to discover, post-breakup, how much he’s taken her lessons to heart. A 26-year-old writer who lives in Williamsburg was dating someone who, she says, “hated New York—he never went out, and the person he dated before me also never went out. So I took it upon myself to introduce him to people, go out, show him around the city.” They broke up in August, and since then this gentleman has become quite the man about town. “This is what bothered me,” said the writer. “He didn’t take the initiative until after we broke up to really enjoy the city, when I wanted to enjoy it with him.”

Liz, the 31-year-old, had a similar experience with another boyfriend, Jamie. “He would go for weeks without leaving Brooklyn. He always thought I was living beyond my means. We broke up and I expected him to be depressed and never leave Brooklyn and be loser-y.”

But Jamie had other ideas. “For some reason as soon as we broke up, he just shed all of that, and was suddenly DJ-ing places. My hippest acquaintances would be like, ‘Oh, I saw Jamie DJ-ing at Lit; it was so fab!’ And I was like, what? How did my ex-boyfriend get cool? It almost felt like I couldn’t imagine anything more offensive. It made me so angry because it was like, you were so boring and depressed when we were dating, and all it took was me dumping you for you to be this fun guy who’s DJ-ing?”

Of course, some of these Butterfly Effect stories seem like twists on the old “it’s not you, it’s me” excuse. Sheila, a 27-year-old who lives in Greenpoint, was dating a guy (“this was our third relationship, and he followed me to New York”) who lived in Bedford-Stuyvesant. “On the 43 bus, it was 30 minutes away. No big deal—I mean, come on!” Also: “He was unemployed, and I was loaning him money.” The distance proved to be too much for this chap, though. “After he decided he didn’t want to see me for the third straight week in a row, I broke up with him. I mean, he could never even make the effort to come to my house anyway.”

Fast-forward eight months, and Sheila started seeing her ex every day in her neighborhood—“standing outside his new girlfriend’s apartment, right in front of my bus stop, smokin’ a cigarette.”

Melissa, a 36-year-old art director, speculated that the security of a long-term relationship can cement in place behaviors that have been present from the beginning, thereby preventing the catepillar-boyfriend from ever passing through the pupal stage. “I think to a certain extent when you’re in a relationship, you don’t worry as much about impressing that person. If you have to get out there and start all over, you suddenly become very aware about how appealing you are to other people. You just sort of realize that you want to make the best impression.” Melissa’s ex, whom she dated for over six years starting when she was 23, always “had these random jobs and was making $24,000 a year. We were living in San Francisco and we were both supposed to move to New York. I got tired of waiting for him. I was like, O.K., you’ll follow me—and he never followed me. When we finally did break up, he totally, massively got all of his shit together. He started studying computer programming and got this crazy job making $120,000 a year and stock options, and he bought this hot rod car—the Steve McQueen Mustang.” While they were dating, Melissa says, any vacations they took were planned by her; she would also advance him the money for the trip, and he would “slowly” pay her back. But after they broke up, “he started going on all these crazy vacations, to India and Thailand.”

One 27-year-old woman who works in publishing is philosophical about what she calls her three and a half “wasted years” with her ex, who got engaged to someone less than a year after they broke up. “This is an arena in which guys shine,” she said. “They just seem to bounce back so much quicker, to be edified by a relationship ending rather than destroyed by it.”

I suggested that men are perhaps just much better at compartmentalizing.

“Yeah!” she said. “That’s what he said, too, when I flipped out on him about it. ‘It’s a different relationship, Rachel.’”

dshafrir@observer.com